1. Field of the Invention
The present invention relates to an integrated semiconductor optical device wherein butt-joined first and second semiconductor optical devices are integrated on an InP substrate, and the first and second semiconductor optical devices have a Be-doped InGaAs contact layer. Specifically, the present invention relates to an integrated semiconductor optical device that can reduce contact resistance while maintaining favorable surface morphology.
2. Background Art
In a III-V compound semiconductor formed on an InP substrate, beryllium (Be) is used as a p-type dopant. Be has a shorter diffusion length than zinc (Zn), which is normally used as a p-type dopant. Therefore, if Be is used as a p-type dopant for an electro-absorptive (EA) optical modulator, the concentration of the dopant diffused into the absorption layer can be lowered. Thereby, the electric field of the absorption layer is equalized, and the quenching characteristics are improved (for example, refer to Y. Miyazaki et, al., Journal of Applied Physics, Vol. 93, No. 7, pp. 3823-3826 (2003)).